Persons who have a deficiency of touch complain that commonly touched objects such as clothing, skin, dishes, steering wheel, toothbrush etc. do not feel “right”. They have increased difficulty handling small, light objects like pins, pencils and buttons, which they cannot maneuver well and tend to drop. When the deficiency of touch is more advanced, they cannot feel objects like small pebbles in the shoes and develop blisters or skin wounds.
Other symptoms that may be experienced by persons with a deficiency of touch include numbness of toes, feet or other skin locations. Abrasions, burns, infections, disequilibrium or motor system problems can result when one is unaware of harmful stimuli. Abnormal touch sensation can be caused by disease or injury to the spinal cord, brain or peripheral nerves. Peripheral nerve damage may be caused by trauma to arms or legs or peripheral neuropathy associated with certain conditions such as diabetes, HIV, herpes (shingles), toxic substances and carpal tunnel.
If the person is diabetic there is a real threat of non-healing sores, gangrene and amputation. Diabetes is the world's most frequent cause of leg amputation, which essentially demobilizes the patient. In underdeveloped countries there is little chance for an amputee to earn a living. In order to decrease the incidence of amputations from diabetic neuropathy, it is important to make an early diagnosis of diabetic neuropathy and measure the degree of severity of the diabetic neuropathy. The length of time that neuropathy has occurred, as well as the degree of nerve fiber damage or loss, contribute to the creation of skin sores, infection and chances of eventual amputation. However, clinicians are not easily able to quantify a deficiency of touch sensation. This problem is compounded in underdeveloped countries.
One easy and fast classical neurological test for touch sensation involves lightly touching the skin with the examiner's fingers or a whisk of cotton and asking if the subject felt the stimulation or if the stimulation felt normal. Any body surface can be tested. However, the stimulus is not calibrated and the results are subjective, non-quantified and not repeatable. Another classical method to test touch sensation uses a calibrated set of “von Frey hairs” (sold commercially as Semmes-Weinstein nylon filaments) of known bending force. Individual nylon filaments are pressed one at a time onto the skin's surface until the filament bends. The threshold can be determined by detecting the filament of lowest bending force on more than 50% of trials. The test is time consuming for each site tested and is subjective. Vibration threshold is usually tested using a tuning fork of known vibration frequency placed on the affected skin and timing the seconds it is perceived. Responses to these stimuli are subjective.
More elaborate expensive devices measure touch threshold using single calibrated stimuli, usually a thin rod that indents the skin by a controlled and known distance with calibrated velocity in a direction perpendicular to the skin's surface. These are similar in principal but better calibrated than the Semmes-Weinstein nylon filaments. Factors that influence the detection of stimuli include the speed of skin indentation, size of stimulated area, amount of pre-indentation and characteristics of repetitive components, if present. Patient response is by forced choice response of whether the stimulus is felt or not felt. Such forced choice responses are time consuming, as a choice is made after each time the rod indents the skin. Several trials are necessary with different stimulus strengths to determine the threshold. These devices are sophisticated electro-magnetic devices that cost several thousand dollars, and require technical and computer support. Testing with these devices almost always requires a patient visit to a special laboratory. They are rarely used in the clinic or at the bedside, even in research institutions.
None of these techniques assess tactile sensory deficit for normal people or people suspected of having lost tactile sensory function by measuring the tactile capacity to detect irregularities on a surface when the surface is moving across the skin or when the skin is moving across the surface even though this is the common means that we humans use to detect or “feel” surfaces or objects.
Dr. Robert LaMotte researched the touch threshold of healthy humans and monkeys using raised dots or bumps of different sizes on otherwise smooth surfaces. Results were gathered from normal young subjects, without testing for variations due to age, sex and race. He did not measure the responses of persons with disease. This work identified an appropriate size and height of bumps on smooth surfaces that could be felt by a normal, healthy human. The work was performed in a controlled, research environment rather than in a practical situation such as a medical clinic or in the field for epidemiology. Measurements did not include the sensory function of the toes.